2.2 Local Calls

Calls within a block, whatever a block is, can use a local
calling convention in which the compiler knows where all of the
values are to be stored, and thus can elide the check for number
of return values, stack-pointer restoration, etc. Alternately,
they can use the full unknown-values return convention while
trying to short-circuit the call convention. There is probably
some low-hanging fruit here in terms of CPU branch-prediction.

The local (known-values) calling convention is implemented by
the known-call-local and known-return VOPs.

Local unknown-values calls are handled at the call site by the
call-local and mutiple-call-local VOPs. The main difference
between the full call and local call protocols here is that
local calls use a different frame setup protocol, and will tend
to not use the normal frame layout for the old frame-pointer and
return-address.